A need exists to provide for better protection and security against counterfeiting and grey-market trading, particularly for pharmaceuticals. A review of counterfeiting in pharmaceuticals and its economic effects may be found in, for example, (1) “Counterfeit Pharmaceuticals: Current Status and Future Projections,” A. I. Wertheimer, N. M. Chaney, T. Santella, J. Am. Pharm. Assoc. 43(6):710-718, 2003, and (2) Chapter 4 of the book “Counterfeiting exposed: protecting your brand and your customers,” D. M. Hopkins, L. T. Kontnik, M. T. Turnage (Wiley, Ed. 2003); ISBN: 0471269905. Chapter 12 describes current anti-counterfeiting methods, such as holograms, intaglio printing, color-shifting technologies, and chemical or biochemical taggants. In many cases, however, most of these prior methods are not appropriate for pharmaceuticals, since they would require the addition of a non-edible or unapproved chemical compound to the tablet or capsule. There is therefore a need for an improved anti-counterfeiting method that does not significantly modify the target pharmaceutical unit.